Vitrectomy surgical apparatus with cut timing based on pressures encountered

ABSTRACT

A vitrectomy apparatus is provided, including a pressure source, a cut valve connected to the pressure source, the cut valve configured to be turned on and off to provide pressure to selectively extend and retract a vitrectomy cutting device, a sensor configured to sense pressure provided from the cut valve, and a controller configured to control operation of the cut valve based on pressure sensed by the sensor. The controller is configured to monitor pressures encountered and alter cut valve timing based on pressure conditions previously encountered.

This application is a divisional of and claims priority to U.S. patentapplication Ser. No. 13/717,021, filed Dec. 17, 2012, the entirecontents of which are incorporated herein by reference.

U.S. patent application Ser. No. 13/717,021 was filed concurrently withthe following applications, both of which are incorporated herein byreference:

“Vitrectomy Surgical Apparatus”, inventors Fred Lee, et al., U.S.application Ser. No. 13/717,071, and issued on Nov. 8, 2016 as U.S. Pat.No. 9,486,358; and

“Vitrectomy Surgical Apparatus with Regulating of Material Processed”,inventors Kyle Lynn, et al., U.S. application Ser. No. 13/717,044, andissued on Mar. 1, 2016 as U.S. Pat. No. 9,271,867.

BACKGROUND

Field

The present invention relates generally to the field of surgical repairof retinal disorders, and more specifically to pneumatic vitrectomyoperation during ophthalmic surgical procedures.

Background

The present invention relates generally to the field of surgical repairof retinal disorders, and more specifically to pneumatic vitrectomyoperation during ophthalmic surgical procedures.

BACKGROUND

Vitrectomy surgery has been successfully employed in the treatment ofcertain ocular problems, such as retinal detachments, resulting fromtears or holes in the retina. Vitrectomy surgery typically involvesremoval of vitreous gel and may utilize three small incisions in thepars plana of the patient's eye. These incisions allow the surgeon topass three separate instruments into the patient's eye to affect theocular procedure. The surgical instruments typically include a vitreouscutting device, an illumination source, and an infusion port.

Current vitreous cutting devices may employ a “guillotine” type actionwherein a sharp-ended inner rigid cutting tube moves axially inside anouter sheathing tube. When the sharp-ended inner tube moves past theforward edge of a side port opening in the outer sheathing tube, the eyematerial (e.g. vitreous gel or fibers) is cleaved into sections smallenough to be removed through the hollow center of the inner cuttingtube. Vitreous cutters are available in either electric or pneumaticform. Today's electric cutters may operate within a range of speedstypically between 750-2500 cuts-per-minute (CPM) where pneumatic cuttersmay operate over a range of speeds between 100-2500 CPM. The surgeon maymake adjustments to control the pneumatic vitrectomy surgical instrumentcutting speed, i.e. controlling the cutting device within the handpiece,in order to perform different activities during the correctiveprocedure. Corrective procedures may include correction of maculardegeneration, retinal detachment, macular pucker, and addressing eyeinjuries.

The cutting device within a pneumatic handpiece requires precise controlof applied pressure to overcome the internal spring return mechanism toassure the quality of each cutting stroke. Today's systems typicallyemploy a constant opening signal time to open the valve at low cuttingspeeds. As the selected cutting speed increases, reducing the amount oftime the valve is opened is often necessary to prevent constantover-pressurizing of the handpiece at the forward end of the cuttingstroke. The frequency of opening and closing the pneumatic valve, i.e.the time interval between each opening cycle of the valve, is varied toachieve the desired cutting speed.

Although most designs use variable valve opening timing and variabletiming between valve openings for pneumatic vitrectomy cutter control,certain advanced designs vary the input pneumatic supply pressure asvitrectomy cutter speed changes. Such operation can enhance the qualityand efficiency of material processed by the vitrectomy cutter duringeach cut cycle. The fundamental limitation of a variable input supplypressure vitrectomy cutter control is the shortest amount of time thatthe air volume in the cutter body and the associated tube set may bepressurized to reach the minimum peak pressure required to advance thecutter to a cut position and then vent to reach the minimum residualpressure to allow the spring-loaded cutter to return to a retractedposition. Again, current pneumatic designs are limited to cutting speedswithin a range of approximately 100 to 2500 CPMs.

Further, current vitrectomy systems typically compensate for mechanicaldelays by providing excess pressure to extend the cutter and/orallocating excess time to retract the cutter. This type of operation isbased on historical performance and some conjecture that the presentsituation is similar to past situations. Such operation and use of powerand/or timing buffers are not optimal. Further, a certain amount ofmaterial is typically brought into the cutter based on the aspirationrate and the amount of time the cutter is open or closed, which isrelated to the pressure supplied to the cutter during each cut cycle.Such designs cut based on scheduled timing, resulting in more or lessmaterial cut than desired.

Today's vitrectomy surgical systems require a wide range of selectablecutting speeds and highly accurate control of the amount of pressuresupplied is desirable to ensure proper instrument handpiece control andsafe use in an operating theater. It may be beneficial in certaincircumstances to offer the surgeon enhanced accuracy in cutting speeds,cutting efficiency, controllability, and other attributes related toperformance of the vitrectomy procedure. Further, in certaincircumstances benefits may be obtained by adjusting operation based onconditions encountered rather than establishing and employingoperational parameters irrespective of such conditions, includingaltering operational parameters such as cut rate, amount of materialcut, and other critical vitrectomy parameters.

Based on the foregoing, it would be advantageous to provide a systemthat enables pneumatic cutting functionality at cutting speeds at orhigher than those achievable with today's vitrectomy surgical instrumentsystems. Such a design would benefit from options offered that providemore effective and efficient cutting parameters as compared with priordesigns.

SUMMARY

Thus according to one aspect of the present invention, there is provideda vitrectomy apparatus including a pressure source, a cut valveconnected to the pressure source, the cut valve configured to be turnedon and off to provide pressure to selectively extend and retract avitrectomy cutting device, a sensor configured to sense pressureprovided from the cut valve, and a controller configured to controloperation of the cut valve based on pressure sensed by the sensor. Thecontroller is configured to monitor pressures encountered and alter cutvalve timing based on pressure conditions previously encountered.

Other features and advantages of the present invention should beapparent from the following description of exemplary embodiments, whichillustrate, by way of example, aspects of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a common vitrectomy system's pneumatic cuttingmechanism, located within a surgical handpiece, with the pneumaticcutting mechanism extended in a “cut,” “closed port,” or “forward”position;

FIG. 1B shows a common vitrectomy system's pneumatic cutting mechanism,located within a surgical handpiece, with the pneumatic cuttingmechanism spring retracted in an “initial,” “open port,” or “backward”position;

FIG. 2A is a graph illustrating a typical cyclical control signal usedfor opening and closing a valve by setting the valve to either anenergizing or a de-energizing state;

FIG. 2B is a graph illustrating an output pressure waveform resultingfrom the control signal illustrated in FIG. 2A;

FIG. 2C is a graph illustrating the cyclical control signal applied to avalve where at a specific instance in time the frequency is increased;

FIG. 2D is a graph illustrating a pressure waveform resulting from thechange in the cyclical control signal frequency as illustrated in FIG.2C;

FIG. 3A is a block diagram illustrating components and devices for apneumatic vitreous cutting module integrated within aphacoemulsification machine in accordance with the present design;

FIG. 3B illustrates a handpiece used in the vitrectomy procedureintended to be used with the variable pressure pneumatic vitrectomycontrol;

FIG. 4 is a view of a pressure source in the form of a pump employablein the present design;

FIG. 5 shows an exploded view of a valve and sensor manifold assemblyemployed in the present design;

FIG. 6 illustrates the valve and sensor assembly assembled for use;

FIG. 7 is the valve and sensor assembly including associated wiring; and

FIG. 8 is a flowchart of operation according to one embodiment of thepresent design.

DETAILED DESCRIPTION

The following description and the drawings illustrate specificembodiments sufficiently to enable those skilled in the art to practicethe system and method described. Other embodiments may incorporatestructural, logical, process and other changes. Examples merely typifypossible variations. Individual components and functions are generallyoptional unless explicitly required, and the sequence of operations mayvary. Portions and features of some embodiments may be included in orsubstituted for those of others.

The present design provides a system and method for high-speed pneumaticvitrectomy control and operation that employs parameters encountered tomore accurately and efficiently cut the vitreous material.

The present design is directed to accurate, reliable, and efficientcontrol of the forward and backward reciprocating motion cutting speedof the blade in a pneumatic vitrectomy handpiece used in a medicalinstrument system. The present design will be discussed herein with aparticular emphasis on a medical or hospital environment, where asurgeon or health care practitioner performs. For example, an embodimentof the present design is a phacoemulsification surgical system thatcomprises an integrated high-speed control module for the vitrectomyhandpiece. The surgeon may adjust or set the cutting speed via agraphical user interface (GUI) module or a foot pedal switch to controlthe high-speed pneumatic vitrectomy handpiece.

System

FIGS. 1A and 1B are high-level conceptual block diagrams illustrating acommon vitrectomy system's pneumatic cutting mechanism located within asurgical handpiece provided for purposes of explaining the presentinvention. FIG. 1A shows the pneumatic cutting mechanism in the “cut,”“closed port,” or “forward” position, while FIG. 1B shows the pneumaticcutting mechanism in the “initial,” “open port,” or “backward” position.Referring to FIG. 1A, construction of pneumatic cutter devices typicallyinvolve a blade 110 positioned to work or operate against a spring 120by inflating and deflating a bladder 130 configured to move blade 110 by‘pushing’ blade 110 forward to a forward position 175 when bladder 130is inflated and ‘pulling’ blade 110 backward using the energy stored inspring 120 to its resting position or initial position 170 when bladder130 is deflated. The desired cutting speed may be realized by fillingand emptying bladder 130 in a cyclical manner through an air passage 140arranged for receiving a pressurized airburst in the direction indicatedat point 150. The received pressurized air burst is then evacuated orvented in direction 160.

Current designs are generally configured to cyclically inflate anddeflate bladder 130 to move blade 110 in a forward direction 180 andbackward direction 190, thus producing the desired cutting action. Acombination input pressurized air supply and output air venting valvemechanism 195, or valve, is represented in FIGS. 1A and 1B.

In order to control the speed of blade 110, currently availablepneumatic designs typically use a control signal to open and close valve195. Valve 195 may be configured to provide a pressurized airburst whenthe valve is open, filling bladder 130 and venting the air withinbladder 130 when the valve is closed to empty the bladder. Increasingthe frequency of the control signal cycling rate, which produces ashorter pressurized air burst time, generally results in an increasedcutting speed, or an increased number of cuts-per-minute as observed atthe knife. A subsequent decrease in control signal cycling rategenerally produces a slower or decreased cutting speed.

Previous designs have employed control signals to drive the cutter. Oneexample control signal to instruct the opening and closing of valve 195associated with air passage 140 is shown in FIG. 2A. The control signalillustrated in FIG. 2A may cycle between valve-off (V_(O)) at point 210and valve-on (V_(E)) at point 220, or provide a valve-energizedinstruction at a predetermined cycling rate, thereby effectuating thedesired cutting speed. FIG. 2B illustrates an example pressure waveformresulting from the application of the control signal shown in FIG. 2A.The waveform is shown to have a constant rise in pressure up to a peakpressure (P_(P)) at 230 when the valve is energized. A subsequent dropin pressure to a residual pressure (P_(R)) at point 240 occurs when thevalve is de-energized. The cycling in pressure, for controlling theblade forward and backward reciprocating movements, as illustrated bythe waveform shown in FIG. 2B, may produce a specific cutting speed forblade 110 in terms of cuts-per-minute.

Pneumatic cutter designs have been configured with a speed controldevice to select and vary the rate the blade mechanism moves forward andbackward to effectuate cutting. In these designs, changing the speed ofthe blade may involve varying the time or duration of the control signalprovided to the valve. By increasing the open period and closed periodof valve 195, the resultant blade speed is reduced. Likewise, decreasingthe amount of time valve 195 is open and closed causes the blade speedto increase.

An example of a control signal for controlling the filling and emptyingof air in bladder 130 with an increase in cycle time is illustrated inFIG. 2C. Before time t₁ at 250, the control signal cyclic frequency isset at a lower rate than after time t₁ to illustrate the surgeonselecting an increase in cutting speed at time t₁ during a surgicalprocedure. FIG. 2D illustrates an example pressure waveform resultingfrom the application of the control signal shown in FIG. 2C. Thispressure waveform reflects the control signal change that occurred attime t₁ at 250, and may drive blade 110 at a faster rate.

The pneumatic vitrectomy handpiece is used in connection with aphaco-vitrectomy module and may be part of a phacoemulsificationmachine. Such a handpiece may include a “guillotine” type cutterpneumatically driven to either an open or closed position. Opening andclosing occurs via air pressure provided via a flexible line or deliveryline between the cutter and a pneumatic driver. The pneumatic driver mayinclude a pressure source, such as a pump, configured to fill a smallreservoir with compressed air at its maximum pressure capacity. Theoutput of this reservoir is connected to a pressure regulator that mayregulate the air pressure down to the level required by the cutter, asshown by peak P_(P) and residual P_(R) pressure in FIG. 2B. A smallerreservoir may be supplied or fed by the regulator output, forming thesource for the delivery valve.

The electronic controller may be connected to the delivery valve and mayprovide instructions to produce a pulse width (in time) of pressurizedair when the valve is open. The controller may be arranged to providefixed pulses of pressurized air within the flexible line in a mannerthat drives the cutter. The electronic controller may use a fixed pulsetiming control signal to instruct the delivery valve to open and close.The fixed timing, or fixed duration, control signal instructs thedelivery valve to open and close in a constant cyclical manner. When theflexible line is at zero or near zero pressure, for example refer toresidual pressure P_(R) shown in FIG. 2B, the cutter is biased towardthe initial or resting position. The cutter closes when the air pressurein the cutter delivery line exceeds a predetermined value between P_(R)and P_(P). When the delivery valve is off, the air in the cutter tubingis exhausted through the valve exhaust port. The cutter then returns tothe initial position when the pressure in the delivery line decreasesclose to atmospheric pressure, i.e. P_(R).

The foregoing description generally discloses the components and controlfunctionality of prior vitrectomy devices. Such control functionalitycan be characterized as “open-loop,” or without any type of feedback.Cutting speeds, etc. are simply set by a surgeon or user andeffectuated, and changes in conditions or parameters in the environmentare unaccounted for.

FIG. 3A is a block diagram illustrating components and devices for aPneumatic Vitreous Cutting Module 305 integrated within aPhacoemulsification Machine 300 in accordance with the present design.Although depicted as an integral unit, module 305 functionality may berealized by using multiple devices to perform the functionalitydisclosed. From FIG. 3A, a Compressed Air Source 310 and associated AirCheck valve 311 may supply air pressure for Pneumatic Vitreous CuttingModule 305. The Compressed Air Source 310 typically comprises a pump(not shown) configured to both provide a pneumatic, typically a gas suchas air, supply pressure to the cut valve and a vent mechanism to relievepressure to atmospheric conditions. Compressed Air Source 310 thusprovides a source of vacuum or pressure. Compressed air is provided bythe pump via Delivery Line 301 illustrated between Air Check valve 311and Pre-Regulator 312. Check valve 311 is typically arranged with twoports and may allow air pressure to flow through in one direction, fromCompressed Air Source 310 to Pre-Regulator 312. The pump may pumppressurized air into a high pressure chamber, not shown, which in turnprovides high pressure air to Pre-Regulator 312 via Delivery Line 301.The high-pressure chamber or Compressed Air Source 310 may provide astable source of air at a higher pressure than the working pressure ofthe cutter.

As used herein, the term “pressure source” or the “Compressed AirSource” means any device or arrangement that is configured to provide asource of pressure or vacuum, including but not limited to a pump orventuri device, compressed air supply, compressed air inlet supply, orany device provided within a vitrectomy machine or originating from anexternal source that provides pressure or vacuum, such as a pressuresource provided through a wall of a building, e.g. via a wall mountednozzle or device, an external pressure source such as an external pump,or otherwise. The terms are therefore intended to be interpretedbroadly.

Pre-Regulator 312 may provide a workable steady air pressure stream fromwhich Compressed Air Source 310 may supply air pressure for PressureRegulator 313 via Delivery Line 302. Pressure Regulator 313 may bepreset to a desired pressure and may be configured to provide air toAccumulator 314 at a low, -steady, and safe operating pressure. PressureRegulator 313 may connect directly to Compressed Air Source 310,typically a pump but alternately a high pressure chamber, by a deliveryline and take input high pressure and regulate the air pressure to alower value consistent with the operating pressure of the cutterhandpiece.

Accumulator 314 may operate as a working pressure chamber, and mayreceive pressurized air at specific pressure and volume from PressureRegulator 313 via Delivery Line 303. Accumulator 314 may provide aspecific amount of air pressure at a predetermined volume to Cut Valve316 via Delivery Line 304 such that no excess pressure is forced intothe Delivery Line 317.

Controller 320, which may provide a graphical user interface, computes acut rate based on physician input and electronically provides a desiredor computed cut rate to Cut Valve 316 via communications Control Line306. The Controller 320 may take different forms, including comprising aPCBA (printed circuit board assembly), or may be part of a PCBA, ASIC,or other hardware design. A storage unit (not shown) may be provided tostore certain values used by the Controller 320 during the vitrectomyprocedure, including settings desired by the surgeon and other relevantdata. Cut Valve 316 may open and close in response to the control signalprovided from Controller 320. Controller 320 electronically controls thevalves operating the regulated pressure and/or vacuum air sent to thecutter. The handpiece blade motion may move in a forward and backwardreciprocating motion in response to the pressure waveform provided viaCutter Tubing 317.

Sensor 315 may monitor the pressure coming from Cut Valve 316 viaDelivery Line 317. Sensor 315 may operate to determine the pressure inDelivery Line 317, and as shown is located between Cut Valve 316 and thecutter (not shown).

During operation, Controller 320 may operate Cut Valve 316 to deliver apulse of regulated air pressure to Delivery Line 317, sensor 315, CutterTubing 318, and cutter (not shown). While the surgeon or practitionermay select variations in the pulse repetition frequency, once theselection is made, the system seeks to attain the desired cutting rate,subject to the discussions herein relating to optimizing cuttingoperation.

Cut Valve 316 is electronically controlled by Controller 320 to transmitpressure, and Cut Valve 316 opens and closes at a precise time to allowair at a specific pressure and volume to fill the Cutter Tubing 317 andoperate the cutter. Cut Valve 316 may connect to atmospheric pressurefor purposes of venting air received from Cutter Tubing 317. Controller320 may provide an electronic indication to Cut Valve 316 thatoriginates with a user selected switch, such as a switch on thehandpiece, graphical user interface, or a foot switch.

Of particular note in the present design is the connection betweenSensor 315 and Controller 320 shown as Line 307. This connection enablesuse of sensed pressure from Cut Valve 316 to be employed to determineprecise commands transmitted to Cut Valve 316. Controller 320 may employpressure sensed, and/or changes in pressure over periods of time, and/orpressure thresholds being exceeded to accurately control overallperformance of the system.

FIG. 3B illustrates a handpiece used in the vitrectomy procedure thatmay be operated with the variable pressure pneumatic vitrectomy control.From FIG. 3B, Cutter Tubing 318 is positioned within an outer passageway352, and the handpiece 350 and pneumatics described above drive the endof cutter tubing 353 back and forth to cut vitreous material. CutterTubing 318 may have a uniform inner and outer diameter.

The present design employs feedback of various parameters and operationspecifically tailored to operation under the specified conditionsencountered based on the parameters fed back and values thereof. Thepresent description is divided into three general sections: Regulatingand optimizing vitrectomy cut pressure, monitoring amount of materialcut to optimize the cutting process, and determining peak and troughpressures to accurately control vitrectomy cutting.

Determination of Cut Pressure

As noted, the vitrectomy system includes a pneumatic pressure supply, acut valve, and a vitrectomy cutter. In operation, previous designs haveprovided a desired cut speed, translated into a desired on and offtiming of a valve used to provide pressure and vent pressure applied tothe bladder. Operation can vary due to pressure issues and mechanicalissues, and to compensate for inherent mechanical issues, a certainamount of additional pressure had been applied, and/or additional timeallocated to retracting the cutter. This compensation based onconjecture tended, in certain circumstances, to produce inefficientcuts.

The present design addresses the cutting inefficiencies by introducing apressure sensing arrangement and a pressure feedback controlarrangement. The present design includes a pressure sensor/transducerand a pressure controller that provide closed-loop operation and furtherprovide an ability to sense pressure and alter performance based ondesired performance criteria.

FIG. 4 is a view of the various pump components, generally referred toas pump 400. Pump 400 includes pump core 401 and pump 400 providespressure via line 401 and nozzle 402. Also shown in this view areelectronic pressure regulator 403 and air filter 404. Electronicpressure regulator 403 is employed to regulate the amount of pressuresupplied by the pump core 401, while air filter 404 filters the air thatis provided to the pump core 401. An oxygen or air source may beprovided (not shown), and this source feeds air filter 404.

FIG. 5 illustrates the valve and sensor manifold 500. From FIG. 5, thenozzle 501 mates with nozzle 402 in FIG. 4, and line 502 connects to cutvalve 503. A small section of tubing 504 is provided that connects thecut valve 503 to the pneumatic manifold 505. Pneumatic manifold 505enables mounting of the various components illustrated to a vitrectomydevice as well as passage of pumped gas. Pneumatic manifold 505 includesan opening, not shown in this view, enabling the pressuresensor/transducer 506 to be introduced. Pressure sensor/transducer 506includes a nozzle 507 and a printed circuit board 508 that enablessensing of pressure and conversion of the sensed pressure to anelectrical value. Placement of the pressure sensor/transducer 506between the cut valve 503 and the vitrectomy handpiece (not shown)enables monitoring of the precise pressure being delivered to the cutterat all times.

The combination sensor and pressure transducer in this arrangementprovides closed loop monitoring of the actual delivery pressureencountered, allowing compensation for variations in cut valveperformance and supply pressures. In short, the combination sensor andpressure transducer receives and determines the pressure in the line anddetermines when to turn the cut valve on and off. FIG. 6 shows theassembled valve and sensor manifold 500, while FIG. 7 shows the valveand sensor manifold 500 with cord 701 extending therefrom. Cord 701provides power to the cut valve 503 as well as the combination sensorand pressure transducer 506, which includes printed circuit board 508.

With respect to the printed circuit board 508, the functionalityrequired is fairly straightforward in that the circuitry must monitorthe pressure coming though nozzle 507 and convert received pressure intoan electronic signal or value, such as a number of psi (pounds persquare inch) or other value. Based on the desired performance, such asthe performance described below, the printed circuit board illustratedor another electronic device, such as another printed circuit board,provides signals to turn on and off cut valve 503. The inputs monitoredand the logic implemented in the printed circuit board arrangement,including printed circuit board 508, is discussed below.

The arrangement of FIGS. 5-7 in addition to the pump of FIG. 4 enabledetection of certain pressure values, including detecting whetherpressure changes have occurred over a period of time, whether pressurehas reached certain thresholds, and other pressure related parametersusable in the vitrectomy procedure. Monitoring of pressure during thecutting phase, when extending the probe, allows for an improved pressurebeing supplied to the cutting device, which eliminates the need toprovide excess pressure or alter timing to compensate for mechanicalissues. Such pressure monitoring can result in the cutter start cyclebeginning sooner, allowing more material to enter the cutter forprocessing during a next cycle, and can provide increased benefits forcutting port opening time.

Thus the present design includes a vitrectomy apparatus having a pump, acut valve connected to the pump, the cut valve configured to be turnedon and off to provide pressure to selectively extend and retract avitrectomy cutting device, a sensor configured to sense pressureprovided from the cut valve, and a controller configured to control thecut valve based on pressure sensed by the sensor.

Monitoring of Material Processed

Using the foregoing apparatus, the surgeon or user may wish to monitorthe amount of vitreous material brought into the cutter. The inabilityto monitor the amount of material provided to the cutter can result inmore or less material cut than is desired. Failure to cut sufficientmaterial decreases the efficiency of the vitrectomy procedure, whilecutting too much material can harm the patient.

The present design also monitors two thresholds, the opening pressurethreshold and the closing pressure threshold. Monitoring of openingpressure ensures that the opening pressure threshold has been achievedand the cutter is open, while monitoring of the closing pressure ensuresthat the closing pressure threshold has been achieved such that thevitrectomy cutter is closed. While the cutter is open, aspiration takesplace and material is drawn into the central lumen of the cutter.

The present design also monitors the pressure supplied to the vitrectomycutter to determine when the cut pressure is between the openingpressure threshold and the closing pressure threshold. Once the cutpressure goes below the opening pressure threshold, the systemdetermines the amount of time elapsed for the cut pressure being betweenthe opening pressure threshold and the closing pressure threshold,called the dwell time parameter. The dwell time parameter corresponds tothe amount of material brought into the cutter during each cut cycle.The dwell time and aspiration rates are used to regulate the amount ofmaterial processed by the cutting device. For example, a high aspirationrate in the presence of a given dwell time indicates more material isbeing processed, while a low aspiration rate in the presence of the samegiven dwell time results in less material being processed. The designtherefore takes these parameters (opening pressure threshold, closingpressure threshold, cut pressure, dwell time, and aspiration) anddetermines the amount of material processed based on these values. Suchmonitoring and information may be provided to the user or surgeon,resulting in excision of a desired amount of material processed.

FIG. 8 illustrates operation of the present aspect of the design. FromFIG. 8, the system determines opening and closing pressure thresholds atpoint 801 and begins monitoring the cut pressure using the closed looppressure feedback mechanism described above and illustrated in FIGS. 4-7at point 802. At point 803, the system determines whether the cutpressure is between the opening and closing pressure thresholds. If not,the system continues to monitor cut pressure; if so, the system begins adwell timer indicating the amount of time the cutter is open at point804. At point 805, the system determines the aspiration, and at point806, the system calculates the amount of material processed based onaspiration rate and dwell time. Point 807 assesses whether the cutpressure is no longer between the opening and closing pressurethresholds, and if so, sets the dwell timer to zero at point 808 andloops back as shown. If the cut pressure remains between the opening andclosing pressure thresholds, the system loops back as shown.

The values determined may be employed to control vitrectomy cutting. Forexample, if more material needs to be cut where the system is operatingat a given aspiration rate and a given dwell time, aspiration rate orcut rate may be increased as long as safe operation is maintained andrisks of such controlled or automatic changes are acceptable.

Determination and Use of Specific Pressure Values

As noted, previous designs have operated open loop, without any type ofpressure feedback. Such systems typically used control algorithmsemploying assumptions of errors encountered during the cuttingprocedure, and in certain instances provided excess pressure to extendthe cutting blade and/or excess time to retract the cutting blade. Suchoperation represents a “best guess” as to expected cutting operation,including buffers seeking to compensate for pressure and/or timinguncertainties encountered in the cutting operation.

The present design illustrated in FIGS. 4-7 provides pressure feedback,and the design seeks to optimize cutting, namely advancing the cuttingblade beginning at a point when pressure is lowest and retracting theblade at a point when pressure is the greatest. In the design of FIGS.4-7, an electronic signal is provided to open and close the cut valve,where the signal is a pulse width modulated signal that had beengenerated from desired cuts per minute set by the user. The presentdesign still obtains a desired number of cuts per minute from the user,but seeks to make the cuts in the most effective way possible.

To perform an accurate cutting, the present system maintains twopressures, namely peak pressure and trough pressure. Peak pressure isthe maximum pressure attained after the command has been given toretract the blade, and represents a maximum expected pressure that willbe encountered. An initial peak pressure may be provided or programmedinto the vitrectomy device, or the maximum pressure may be employed whenthe first retraction occurs and changed as necessary at a later time. Ifthe peak pressure measured during a given retraction of the cuttingblade is greater than the peak pressure maintained by the system, thesystem replaces the maintained peak pressure value with the mostrecently encountered peak pressure value. In this manner the highestpeak pressure encountered will always be maintained.

Conversely, trough pressure is the minimum pressure encountered afterthe command has been given to advance the blade. An initial troughpressure may be provided or the first trough pressure encountered may bestored as the baseline trough pressure. If the trough pressure measuredduring a given extension period is less than the trough pressuremaintained by the system, the system replaces the maintained troughpressure value with the most recently encountered trough pressure value.Such operation ensures that the lowest trough pressure encounteredduring a procedure is employed.

The system also operates a timer such that the time between sending thecommand to extend or retract the cutting blade and acquisition of thepeak or trough pressure can be measured. The time between a command andthe system attaining either peak or trough pressure may also bemaintained in the system.

With the highest encountered peak pressure and lowest encountered troughpressure, the system can act to accurately initiate cut blade extensionand retraction times. As an example, assume that the peak pressureencountered during a current procedure is X psi and the time between thecommand and the system attaining this peak pressure is Y milliseconds.If the desired cut rate is Z cuts per second, the system anticipatesthat after a command to retract the blade, it will take Y millisecondsto reach a peak pressure X psi. The system thus alters the timing of theretract command such that the system will retract the blade at the timewhen peak pressure will occur.

Alternately, the system may monitor current pressure and may use themaintained peak pressure and trough pressure as triggers. In thisembodiment, if the command has not been given by the time the peakpressure or trough pressure has been attained, the system issues theretract or extend command.

As a further option, the system may, for example, determine a maximumpressure of X psi occurs Y milliseconds after issuing a retract command.The system may monitor the pressure encountered when the command issues,which may be, for example, 0.9*X. Should the system encounter this 0.9*Xpressure at a time after an extend command has been given, the systemmay issue the retract command, seeking to obtain the maximum maintainedpressure at a desired time.

Such variations give the operator the ability to have a higher level ofconfidence that cuts (extensions and retractions of the blade) willoccur at or near an optimal time based on the commanded cut rate. Thusthe present system includes a vitrectomy apparatus having a pump, a cutvalve connected to the pump, the cut valve configured to be turned onand off to provide pressure to selectively extend and retract a cuttingdevice, a sensor configured to sense pressure provided from the cutvalve, and a controller configured to control the cut valve based onpressure sensed by the sensor, wherein the controller monitorsencountered pressures and alters cut valve timing based on pressureconditions previously encountered.

Those of skill in the art will recognize that any step of a methoddescribed in connection with an embodiment may be interchanged withanother step without departing from the scope of the invention. Those ofskill in the art would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed using a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such the processorcan read information from, and write information to, the storage medium.In the alternative, the storage medium may be integral to the processor.The processor and the storage medium may reside in an ASIC. The ASIC mayreside in a user terminal. In the alternative, the processor and thestorage medium may reside as discrete components in a user terminal.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. A method for performing a vitrectomy procedure,comprising: sensing pressure provided from a pressure source through acut valve and to a vitrectomy handpiece; and controlling operation ofthe cut valve based on pressure sensed; wherein controlling operation ofthe cut valve based on pressure sensed comprises monitoring andmaintaining a peak pressure value and a trough pressure value andaltering cut valve timing based on pressure conditions previouslyencountered; wherein the peak pressure value represents a maximumpressure encountered and the trough pressure value represents a minimumpressure encountered.
 2. The method of claim 1, wherein controllingoperation of the cut valve comprises altering cut valve timing based ona pressure encountered relative to the peak pressure valve and thetrough pressure value.
 3. The method of claim 2, wherein controllingoperation of the cut valve comprises monitoring a time starting fromissuing a command to the cut valve and one from the group consisting ofthe peak pressure value and the trough pressure value, and altering afuture command time for a future command issued to the cut valve basedon the time.
 4. The method of claim 3, wherein controlling operation ofthe cut valve comprises issuing the command to the cut valve when thepressure encountered reaches a threshold pressure calculated based onthe time and one from the group consisting of peak pressure value andthe trough pressure value.
 5. The method of claim 3, wherein controllingoperation of the cut valve comprises setting the peak pressure to be apresently encountered peak pressure when the presently encountered peakpressure is greater than any previously encountered peak pressure. 6.The method of claim 3, wherein controlling operation of the cut valvecomprises setting the trough pressure to be a presently encounteredtrough pressure when the presently encountered trough pressure is lessthan any previously encountered trough pressure.
 7. The method of claim1, wherein the cut valve is pneumatically connected to a pump, a sensor,and the vitrectomy handpiece.